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Message-ID: <301c7fb7d22ad6ef97856b421873e32c2239d412.camel@linux.intel.com>
Date: Wed, 22 Jul 2020 12:56:10 -0700
From: Kristen Carlson Accardi <kristen@...ux.intel.com>
To: Kees Cook <keescook@...omium.org>, Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Miroslav Benes <mbenes@...e.cz>, tglx@...utronix.de, mingo@...hat.com,
bp@...en8.de, arjan@...ux.intel.com, x86@...nel.org,
linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
rick.p.edgecombe@...el.com, live-patching@...r.kernel.org
Subject: Re: [PATCH v4 00/10] Function Granular KASLR
On Wed, 2020-07-22 at 12:42 -0700, Kees Cook wrote:
> On Wed, Jul 22, 2020 at 11:07:30AM -0500, Josh Poimboeuf wrote:
> > On Wed, Jul 22, 2020 at 07:39:55AM -0700, Kees Cook wrote:
> > > On Wed, Jul 22, 2020 at 11:27:30AM +0200, Miroslav Benes wrote:
> > > > Let me CC live-patching ML, because from a quick glance this is
> > > > something
> > > > which could impact live patching code. At least it invalidates
> > > > assumptions
> > > > which "sympos" is based on.
> > >
> > > In a quick skim, it looks like the symbol resolution is using
> > > kallsyms_on_each_symbol(), so I think this is safe? What's a good
> > > selftest for live-patching?
> >
> > The problem is duplicate symbols. If there are two static
> > functions
> > named 'foo' then livepatch needs a way to distinguish them.
> >
> > Our current approach to that problem is "sympos". We rely on the
> > fact
> > that the second foo() always comes after the first one in the
> > symbol
> > list and kallsyms. So they're referred to as foo,1 and foo,2.
>
> Ah. Fun. In that case, perhaps the LTO series has some solutions. I
> think builds with LTO end up renaming duplicate symbols like that, so
> it'll be back to being unique.
>
Well, glad to hear there might be some precendence for how to solve
this, as I wasn't able to think of something reasonable off the top of
my head. Are you speaking of the Clang LTO series?
https://lore.kernel.org/lkml/20200624203200.78870-1-samitolvanen@google.com/
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